Synchronous digital logic circuits, such as those in secure communications devices, for example, may require a clock signal. The digital logic circuit may be an integrated circuit, such as a microchip, application specific integrated circuit (ASIC), or the like. The clock signal may provide a common timing, so that the individual electronic logic components work together properly.
Typically, the clock signal may be provided by an electronic oscillator. For example, a relaxation oscillator, a crystal oscillator, or the like, may produce an electronic signal or waveform. A relaxation oscillator may use analog components such as transistors, capacitors, inductors, or the like to create the waveform. A crystal oscillator may resonate a quartz crystal to create the waveform. Because the oscillators may use non-digital components, they may often be found external to the digital logic microchip.
The generated waveform may be a square wave, having square edges that transition from a high level to a low level and back again regularly over time. The transitions of the square wave may establish the common timing for the digital logic circuitry.
The use of an oscillator in a digital logic circuit application may degrade the efficiency of the overall design. For example, the oscillator may increase the number of electronic components, making the circuit more complex, physically larger, and more costly. The oscillator may increase power consumption of the circuit. Furthermore, because the digital logic circuit depends on the oscillator for timing, some electronics may not work when the oscillator is disabled.
Digital logic circuits may be vulnerable when their external oscillator is compromised. For example, a digital logic circuit required for the protection of sensitive, encrypted data may fail because of malicious tampering with the oscillator on which it depends.